Optical ring resonators (also termed microring resonators) can be used to filter, modulate and switch optical signals. Mechanical and/or electrical contacts to a microring resonator are essential for many applications. Such contacts, however, can perturb the resonant modes of light circulating in the microring resonators; and this can result in propagation losses of the light which can significantly reduce a quality factor (Q) of the microring resonator. This reduction in the Q of the microring resonator limits the utility of the resonator for many applications including communications where a large resonator Q is needed for narrowband filtering, switching, or modulation. What is needed is a way of making low-loss mechanical and electrical connections to microring resonators which preserves a large resonator Q and which also allows the microring resonator to be made with a small size to provide a large free-spectral range (FSR).
The present invention provides a solution to these needs by providing optical ring resonator devices in which mechanical and/or electrical contacts are made from inside of each optical ring resonator therein so that the Q of each ring resonator is preserved and so that the size of each ring resonator can be reduced to as small as 2-3 μm radius.
In certain embodiments of the present invention, an optical waveguide ring in the optical ring resonator device can have a non-uniform width which adiabatically varies between a maximum value and a minimum value. By contacting the optical waveguide ring from the inside thereof at a location near the maximum value of the width, the resonant modes of the light circulating in the optical waveguide ring is not substantially perturbed. This allows either an electrical heater or a semiconductor junction to be located inside the optical waveguide ring for use in varying (i.e. tuning) a resonant frequency therein while maintaining a high resonator Q.
The optical ring resonator devices of the present invention can be formed from silicon using conventional silicon integrated circuit (IC) processes. This allows one or more of the devices of the present invention to be co-located on a conventional silicon-on-insulator substrate together with integrated electronic circuitry to provide a capability for optical signal routing, switching, filtering and detection.
These and other advantages of the present invention will become evident to those skilled in the art.